1. Field of the Invention
The present invention relates to a substrate processing system for performing a batch process, such as a batch cleaning process, on substrates, such as semiconductor wafers;. The present invention also relates to a substrate transfer method used in the substrate processing system and a computer readable medium that stores a program for realizing the substrate transfer method.
2. Description of the Related Art
In the sequence of manufacturing semiconductor devices, a cleaning process is performed by treating a semiconductor wafer (which may be simply referred to as “wafer” hereinafter) with a process liquid, such as a predetermined chemical liquid or purified water to remove contaminants, such as particles, organic contaminants, and/or metal impurities, from the wafer.
As cleaning process systems for performing cleaning processes of this kind, batch type processing systems for processing a plurality of wafers together at a time are frequently used to improve the throughput. The batch cleaning process systems of this kind encompass systems of a FOUP-less type as a main stream in light of compactness of process vessels and shortening of the process time (for example, Jpn. Pat. Appln. KOKAI Publication No. 2002-64075). In the FOUP-less type, a plurality of semiconductor wafers stored in a FOUP (Front Open Unified Pod) are taken out from the FOUP, and are processed while they are held together and immersed in liquid inside a process vessel, so as to decrease the size of the process vessel and shorten the process time.
A batch cleaning process system of the FOUP-less type includes a load port section for loading and unloading FOUPs each storing a plurality of wafers, and for stocking the FOUPs. The system further includes a process section for performing a cleaning process on the wafers, and an interface section for transferring the wafers between the load port section and process section. For example, the system conducts the process sequence, as follows.
At first, a FOUP storing a plurality of wafers is transferred by a FOUP transfer apparatus disposed in the load port section to an access area between the load port section and interface section. Then, some operations are performed at the access area to, e.g., open the lid of the FOUP and to examine the array state of the wafers. Then, the wafers are taken out together from the FOUP by a handling apparatus disposed in the interface section, and are transferred at a wafer load position onto a wafer transfer mechanism for transferring the wafers to the process section. Then, the wafers are transferred by the wafer transfer mechanism to respective process vessels disposed in the process section. After the cleaning process, the wafers are transferred by the wafer transfer mechanism to a wafer unload position in the interface section. In the interface section, the wafers are picked up from the wafer transfer mechanism by the handling apparatus. In the load port section, an empty FOUP is transferred by the FOUP transfer apparatus to the access area, and the lid of the FOUP is then set opened. The wafers picked up from the wafer transfer mechanism by the handling apparatus disposed in the interface section are inserted in the FOUP in the access area. The FOUP with the wafers thus inserted is transferred by the FOUP transfer apparatus to a predetermined position in preparation for unloading.
A process sequence on one lot of wafers is thereby completed in accordance with the sequence described above. In this sequence, transfer of the wafers is controlled by collectively administrating a series of operations, such as the operation of the FOUP transfer apparatus in the load port section, the operations at the access area, such as opening/closing of the lid of the FOUP, and the operation of the wafer handling apparatus. In this way, the process is repeatedly performed on a plurality of lots at certain operation timings. This allows the cleaning process to be performed with simple control.
However, where a plurality of lots are sequentially performed by use of such a constant recipe, a subsequent lot of wafers needs to be loaded at a timing to prevent the schedules from overlapping with each other on the same apparatus at the same time. For example, even where the FOUP transfer apparatus is unoccupied, if a downstream portion of the transfer schedule, such as a schedule portion concerning the wafer handling apparatus, overlaps with the other, the subsequent lot of wafers cannot be loaded, but has to wait until an appropriate timing that prevents any overlap of use of the apparatuses. Consequently, the apparatuses cannot be effectively used in terms of their unoccupied periods, resulting in a decrease in the process throughput.